E. Suchart Upatham

Field studies on the transmission of the human liver fluke, Opisthorchis viverrini, in northeast Thailand: population changes of the snail intermediate host.

Abstract Field studies on the transmission of the human liver fluke, Opisthorchis viverrini , in northeast Thailand: population changes of the snail intermediate host. International Journal for Parasitology 16 : 545–552. A natural population of Bithynia siamensis goniomphalos , snail vector of the human liver fluke Opisthorchis viverrini was sampled for 3 years in a shallow reservoir in Khon Kaen Province, northeast Thailand. During the study period, the habitat experienced a 17-month drought followed by a surging flood. Snails suffered over 90% mortality during drying of the reservoir but died at an average rate of only 5% per month during aestivation. When water returned they migrated to new edge habitats, apparently on floating debris, and reproduced. Peaks in reproduction occurred following spring rains and after the fall monsoon flooding subsided. Normally, two generations are produced per year in seasonal habitats. The prevalence of O. viverrini infection averaged 0.11 % in adult snails over 8 mm in length; smaller snails were not infected. Control of opisthorchiasis through snail control does not appear practical because of the widespread distribution of the snails, their ability to survive in very unstable habitats, and for other reasons concerned with the existence of the fish host between snail and human hosts.

Molecular cloning and characterization of cathepsin L encoding genes from Fasciola gigantica

In this study cDNAs encoding cathepsin L-like proteins of Fasciola gigantica were cloned by the reverse transcription polymerase chain reaction method (RT-PCR) from total RNA of adult specimens. DNA sequence analyses revealed that six different cathepsin L cDNA fragments were isolated, which have DNA sequence identities of 87-99% towards the homologous genes from F. hepatica. Gene expression was studied at the RNA level by Northern and RNA in situ hybridizations. Northern analysis showed the cathepsin L genes to be strongly expressed in adult parasites as a group of 1050 nt sized RNAs. RNA in situ hybridization localized cathepsin L RNA to the cecal epithelial cells. Southern hybridization was used to determine the number of cathepsin L genes and indicated the presence of a family of closely related cathepsin L genes in the genome of F. gigantica.

Phytoaccumulation and Phytotoxicity of Cadmium and Chromium in Duckweed Wolffia globosa

ABSTRACT The phytoaccumulation and phytotoxicity of heavy metals, cadmiun (Cd), and chromium (Cr) on a common duckweed, Wolffia globosa, were studied. W. globosa were cultured in 3% Hoaglands nutrient medium, which was supplemented with 1, 2, 4, and 8 mg/L of Cd and Cr and were separately harvested after 3, 6, 9, and 12 days. The accumulation of Cd and Cr in W. globosa showed significant increases when the exposure time and metal concentration were increased. The effects of Cd and Cr on the biomass productivity and total chlorophyll content in W. globosa indicated that there were significant decreases in the biomass productivity and total chlorophyll content when the exposure time and metal concentration were increased.

DNA-Sequence Variation Among Schistosoma mekongi Populations and Related Taxa; Phylogeography and the Current Distribution of Asian Schistosomiasis

Background Schistosomiasis in humans along the lower Mekong River has proven a persistent public health problem in the region. The causative agent is the parasite Schistosoma mekongi (Trematoda: Digenea). A new transmission focus is reported, as well as the first study of genetic variation among S. mekongi populations. The aim is to confirm the identity of the species involved at each known focus of Mekong schistosomiasis transmission, to examine historical relationships among the populations and related taxa, and to provide data for use (a priori) in further studies of the origins, radiation, and future dispersal capabilities of S. mekongi. Methodology/Principal Findings DNA sequence data are presented for four populations of S. mekongi from Cambodia and southern Laos, three of which were distinguishable at the COI (cox1) and 12S (rrnS) mitochondrial loci sampled. A phylogeny was estimated for these populations and the other members of the Schistosoma sinensium group. The study provides new DNA sequence data for three new populations and one new locus/population combination. A Bayesian approach is used to estimate divergence dates for events within the S. sinensium group and among the S. mekongi populations. Conclusions/Significance The date estimates are consistent with phylogeographical hypotheses describing a Pliocene radiation of the S. sinensium group and a mid-Pleistocene invasion of Southeast Asia by S. mekongi. The date estimates also provide Bayesian priors for future work on the evolution of S. mekongi. The public health implications of S. mekongi transmission outside the lower Mekong River are also discussed.

The distribution of Mekong schistosomiasis, past and future: preliminary indications from an analysis of genetic variation in the intermediate host.

Neotricula aperta is the only known intermediate host of Schistosoma mekongi which infects humans in Cambodia and the southern tip of Lao PDR. DNA-sequence data (partial rrnL, i.e., mitochondrial 16S large ribosomal-RNA gene) were obtained for 359 N. aperta snails sampled at 31 localities in Cambodia, Lao PDR and Thailand. A nested clade analysis was performed to detect and evaluate any geographical patterns in the observed variation and to identify genetic subpopulations or clades. Coalescent simulations were used to compare different historical biogeographical hypotheses for N. aperta and S. mekongi. A coalescent based method was also used to provide maximum likelihood estimates (MLEs) for effective populations sizes and historical growth and migration rates. Dates were also estimated for phylogenetic events on the gene tree reconstructed for the sampled haplotypes (e.g. the time to most recent common ancestor). N. aperta was found to be divided into two monophyletic clades, a spring-dwelling form of northern Lao PDR and a more widespread larger-river dwelling form of southern Lao PDR and Cambodia; this divergence was dated at 9.3 Ma. The populations with the largest estimated population sizes were found in the Mekong River of Lao PDR and Cambodia; these, together with those of the rivers of eastern Cambodia, appeared to have been the fastest growing populations. Dominant levels of gene-flow (migration) were apparent in a South to North direction, particularly out of seeder populations in the Cambodian Mekong River. The radiation of N. aperta into sub-clades across Cambodia and Lao PDR is dated at around 5 Ma. The findings suggest that historical events, rather than ecology, might best explain the absence of S. mekongi from most of Lao PDR. The public health implications of these findings are discussed, as are pointers for future studies and surveillance.

The phylogeography of Indoplanorbis exustus (Gastropoda: Planorbidae) in Asia

BackgroundThe freshwater snail Indoplanorbis exustus is found across India, Southeast Asia, central Asia (Afghanistan), Arabia and Africa. Indoplanorbis is of economic importance in that it is responsible for the transmission of several species of the genus Schistosoma which infect cattle and cause reduced livestock productivity. The snail is also of medical importance as a source of cercarial dermatitis among rural workers, particularly in India. In spite of its long history and wide geographical range, it is thought that Indoplanorbis includes only a single species. The aims of the present study were to date the radiation of Indoplanorbis across Asia so that the factors involved in its dispersal in the region could be tested, to reveal potential historical biogeographical events shaping the phylogeny of the snail, and to look for signs that I. exustus might be polyphyletic.ResultsThe results indicated a radiation beginning in the late Miocene with a divergence of an ancestral bulinine lineage into Assam and peninsular India clades. A Southeast Asian clade diverged from the peninsular India clade late-Pliocene; this clade then radiated at a much more rapid pace to colonize all of the sampled range of Indoplanorbis in the mid-Pleistocene.ConclusionsThe phylogenetic depth of divergences between the Indian clades and Southeast Asian clades, together with habitat and parasitological differences suggest that I. exustus may comprise more than one species. The timescale estimated for the radiation suggests that the dispersal to Arabia and to Southeast Asia was facilitated by palaeogeographical events and climate change, and did not require human involvement. Further samples from Afghanistan, Africa and western India are required to refine the phylogeographical hypothesis and to include the African Recent dispersal.

Opisthorchis viverrini infection in rural and urban communities in northeast Thailand

The prevalence and intensity of liver-fluke (Opisthorchis viverrini) infection were investigated among 559 patients who were born in, and had lived all their lives in, either the rural or urban northeastern Thailand. 344 (79.4%) of 433 rural dwellers were infected compared with only 69 (54.8%) of 126 urban dwellers (P less than 0.005). The intensity of infection, and the reported level of consumption of koi-pla, a favourite dish of local inhabitants prepared from uncooked freshwater fish which often contains viable metacercariae, were greater among rural dwellers than their urban counterparts (P less than 0.05 to P less than 0.005). Infection due to O. viverrini appears to be mainly a rural problem strongly associated with the habit and frequency of eating koi-pla.

Measurement of incidence of the human liver fluke, Opisthorchis viverrini, in northeast Thailand

A survey of a community in northeast Thailand where Opisthorchis viverrini is endemic permitted comparison of two methods of measuring incidence: direct determination of the rate at which an uninfected group became infected between two surveys a year apart, and estimation of incidence from age-specific prevalence data using a logarithmic regression method. Both methods revealed that incidence increased with age in young children, and estimation from age-prevalence data showed that the increase was roughly linear from near birth to about age 5 years, beyond which no clear trend in incidence was evident. A catalytic infection model incorporating an infection rate increasing from birth to age 5, and remaining constant thereafter, gave an excellent fit to age-prevalence profiles. Both methods of determining incidence are sensitive to errors in diagnosis, but the direct determination method is more sensitive to the presence of false negatives. A method for correcting this bias is given. The regression method, which was less sensitive to yearly variation in incidence and is easier to use, is recommended for preliminary surveys to identify villages with high transmission intensity.

Liver procollagen prolyl hydroxylase in Opisthorchis viverrini infected hamsters after praziquantel administration.

Infection of hamsters by the human liver fluke Opisthorchis viverrini elevated liver procollagen prolyl hydroxylase activity, reflecting increased collagen biosynthesis. The increase was proportional to the intensity of infection. However, the infected liver procollagen prolyl hydroxylase activity decreased after administration of praziquantel 300 mg kg-1 body weight, and approached normal levels two weeks after treatment. In the infected hamsters, praziquantel, at a curative dose, caused a transient increase in serum aminotransferase levels and a small but persistent rise in serum alkaline phosphatase. The drug, however, did not cause changes in these enzyme activities in the uninfected hamsters.

Biosorption of Cadmium and Chromium in Duckweed Wolffia globosa

ABSTRACT The biosorption of cadmium (Cd) and chromium (Cr) by using dried Wolffia globosa biomass were investigated using batch technique. The effects of concentration and pH solution on the adsorption isotherm were measured by determining the adsorption isotherm at initial metal concentrations from 10 to 400 mg/L and pH 4 to 7 for Cd, and pH 1.5 to 6 for Cr. The adsorption equilibria were found to follow Langmuir models. The maximum adsorption capacity (Xm) at pH 7 in W. globosa - Cd system was estimated to be 80.7 mg/g, while the maximum removal achieved at pH 4, pH 5, and pH 6 were 35.1, 48.8, and 65.4 mg/g, respectively. The Xm at pH 1.5 in W. globosa - Cr system was estimated to be 73.5 mg/g, while the maximum removal achieved at pH 3, pH 5, and pH 6 were 47.4, 33.1, and 12.9 mg/g, respectively. The effects of contact times on Cd and Cr sorption indicated that they were absorbed rapidly and more efficiently at lower concentrations.